Jay Yarow thought the numbers in the NPD and comScore reports were fishy, so he did the math himself:

Total it all up, and Apple had 63% of the smartphone market on those three big carriers. Verizon, Sprint, and AT&T account for ~80% of the overall wireless market in the U.S., according to a Yankee Group report from August. If Apple accounted for 63% of 80% of the smartphone sales on those carriers, then it had 50% of the total smartphone market in the U.S. in the first quarter of the year. So, how did NPD get to its number of 29%? We asked, and the answer wasn’t all that satisfying.